Mastering Biology Chapter 6

How do cells replace the energy-rich ATP that is destroyed in energy-coupled reactions?

-Chloroplasts use light energy to synthesize ATP. -Mitochondria synthesize ATP using energy that's released by oxidizing sugars and fats.

How can "induced fit" influence the specificity of an enzyme?

-It moves the reactive portion of the enzyme closer to the substrate. -The enzyme's active site changes shape to fit the correct substrate but not other molecules.

Which type of control agent exerts noncompetitive inhibition?

-Protein kinase -Allosteric effector

When allosteric effector X binds to enzyme #1, the enzyme stops working. Nevertheless, the speed of the reaction can be altered by adjusting the concentration of X. How?

-When X detaches from an enzyme, the enzyme regains full activity. - X easily escapes from the allosteric site. -There are many copies of the enzyme.

A reaction is said to be unfavorable if ...

-the free energy change for the reaction is positive -equilibrium favors the reactants, not the products.

Enzymes:

... may change shape when they bind substrates; ...provide no energy for the reaction, except collision energy; ...may release substrates.

Factors that affect an enzyme:

1. An enzyme is denatured when it loses its native conformation and its biological activity. 2. An enzyme is considered a catalyst because it speeds up chemical reactions without being used up. 3. An enzyme is considered specific because of its ability to recognize the shape of a particular molecule. 4. A cofactor, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES)complex. 6. A substrate binds to an enzyme at the active site, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a substrate.

What are the different parts of an ATP molecule?

1. The gamma-phosphate is the third phosphate group and is attached to the beta-phosphate, farthest from the ribose sugar, where it is most likely to participate in energy-releasing reactions. 2. The adenine group is the nitrogenous base attached to the ribose sugar. 3. The alpha-phosphate is the phosphate group closest to the ribose sugar. 4. The beta-phosphate is the phosphate group attached to the alpha-phosphate. 5. The ribose sugar is the scaffold that provides the backbone for the entire adenosine triphosphate molecule.

Enzyme inhibitors:

A (n)competitive inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate. 2. A (n)noncompetitive inhibitor binds to a site on the enzyme that is not the active site. 3. Usually, a(n) irreversible inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the active site on the enzyme. 5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the enzyme is distorted. 6. Enzyme inhibitors disrupt normal interactions between an enzyme and its substrate.

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again?

A competitive inhibitor has a structure that is so similar to the substrate that it can bind to the enzyme in the same way as the substrate.

In cells, what is usually the immediate source of energy for an endergonic reaction?

ATP! The hydrolysis of ATP provides the energy needed for an endergonic reaction.

In an experiment with an enzyme, the 58th amino acid seems to form a covalent bond with a substrate molecule as part of the catalytic process. What would you say?

At some point the bond between the amino acid and the substrate must break.

Which fact is most important in explaining how enzymes speed reactions?

High-energy collisions are less common than low-energy collisions.

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

Hydrolysis: involves breaking bonds with the addition of water.

What is the fate of the phosphate group that is removed when ATP is converted to ADP?

It is acquired by a reactant in an endergonic reaction. note: by acquiring the phosphate group the reactant acquires energy.

Allosteric effectors..

May not resemble the enzymes substrates

Enzymes are what?

Proteins (organic catalyst) -work by reducing the energy of activation

Which type of control agent never speeds an enzyme's action?

Substrate analog (substrate analogs resemble the substrate enough to bind to the active site, but they can't react. Accordingly, they just block the active site and slow the reaction.)

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme?

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

Which of the following is the most logical way to regulate an enzymatic pathway if you are trying to keep a constant level of product around?

The final product inhibits the first enzyme.

How do cells use ATP to raise the energy level of reaction substrates?

The terminal phosphate of ATP is bound to the substrate. (The bond between Pi and the substrate preserves much of the energy that was in ATP.)

The reaction A → B is unfavorable by itself, but through energy-coupling, cells can use ATP to convert A into B. How is this done?

The unfavorable reaction is replaced by two favorable reactions. -The first reaction transfers part of ATP to A, making a high-energy product. That product is then converted to B. Both reactions release energy, so both are favorable.

Why is ATP a good source of energy for biological reactions?

Triphosphate chains are unstable.

When a pathway is subject to allosteric feedback inhibition, ...

an accumulation of effectors slows the pathway.

Which of these is exhibiting kinetic energy? a. the high-energy phosphate bonds of a molecule of ATP b. a space station orbiting Earth c. a person sitting on a couch while watching TV d. an archer with a flexed bow e. a rock on a mountain ledge

b. a space station orbiting Earth

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?

cellular respiration..... This is the name given to the process by which the body converts food energy to energy stored in ATP.

The hydrolysis of ATP provides the energy needed for an endergonic reaction.

endergonic NOTE: Energy has been acquired from the surroundings.

Which of these reactions requires a net input of energy from its surroundings?

endergonic... The products of endergonic reactions have more potential energy than the reactants

"Conservation of energy" refers to the fact that _____.

energy cannot be created or destroyed but can be converted from one form to another

Which statement is true of enzymes?

enzymes can be either proteins or RNA molecules. -When a cell makes an enzyme, it makes many copies. -Their substrate specificity involves matching of shapes.

Select the INCORRECT association. enzyme ... protein exergonic ... uphill exergonic ... spontaneous potential energy ... positional energy kinetic energy ... motion

exergonic ... uphill

The energy for an endergonic reaction comes from a(n) _____ reaction.

exergonic note: The energy released by an exergonic reaction can be used to drive an endergonic reaction.

A(n) _____ reaction occurs spontaneously.

exergonic. In exergonic reactions the products have less potential energy than the reactants.

The following reaction A --> B + C + heat is a(n) _____ reaction.

exergonic... energy is being released!

Which of these are by-products of cellular respiration?

heat, carbon dioxide, and water

Select the highest energy form of adenosine from the following images. Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds.

http://www.easynotecards.com/uploads/256/19/1a051c84_148803f3445__8000_00000510.jpg Adenosine triphosphate (ATP) is made up of three main structural parts: the nitrogenous base adenine, the ribose sugar, and the three phosphate groups bonded together by phosphodiester bonds

The higher the activation energy, the ___________ product formed per unit time.

less

Enzymes speed reactions mainly by ...

lowering EA. -More collisions can produce at the transition state

Chemical energy is a form of _____ energy

potential. Chemical energy is a form of stored energy

What name is given to the reactants in an enzymatically catalyzed reaction?

substrate

Which factors affect enzyme activity?

temperature pH inorganic ions and vitamins

What happens in feedback control?

the first enzyme of a pathway is often allosteric, and a final product of the pathway is the enzyme's allosteric inhibitor

What is energy coupling?

the use of energy released from an exergonic reaction to drive an endergonic reaction

As a result of its involvement in a reaction, an enzyme _____.

unchanged

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

γ-phosphate (the terminal phosphate); the primary phosphate group on the ATP molecule that is hydrolyzed when energy is needed to drive anabolic reactions. Located the farthest from the ribose sugar, it has a higher energy than either the α- or β-phosphate.